The invention relates to a circuit for eliminating current noises produced by a d.c. motor.
In an electrical circuit using a d.c. motor, the waveform of the current flow through the circuit varies as the electrical contact between the brush and commutator of the motor is interrupted during rotation thereof. The variation in the current flow represents an a.c. noise, which may have an adverse influence upon other electrical circuits through the power source. By way of example, in an electroacoustic apparatus such as a tape recorder, the use of a common d.c. source for the tape driving motor and the record and/or playback circuit results in introducing the a.c. noises produced by the motor into the record-playback circuit through the power source, which is then amplified by the associated amplifier to degrade the fidelity of an audio signal. Thus, it should be apparent that the current noises produced by the d.c. motor must be eliminated when a common power source is used for the motor and other electrical circuits.